1. Field of the Invention
The present invention relates to a high temperature heating sputtering process, more particularly, it relates to a high temperature heating sputtering process which provides a sputter-deposited metal film having improved properties.
2. Description of the Related Art
In general, the metal wiring material of a semiconductor device, is made of, for example, an aluminum and an aluminum alloy, e.g., an aluminum alloy containing about 1 to 2% silicon.
Recent development in the degree of integration and high density of semiconductor device elements have resulted in an even greater miniaturization of such elements, and thus the aspect ratio, i.e., the ratio of depth to width of a contact hole formed in the substrate, has become greater. The contact hole forms a step in a metal wiring region of a semiconductor device, and due to this increase of the aspect ratio, the step coverage of a contact hole has become difficult.
In general, a sputtering process is used to deposit an aluminum and an aluminum alloy, sputtered from a target thereof, onto a substrate as a metal wiring material, and to improve the step coverage, a high temperature heating sputtering process has been developed wherein sputtering is carried out while a substrate, e.g., a silicon wafer is kept at a high temperature of, for example, 500.degree. to 600.degree. C. In this high temperature heating sputtering process, the substrate is heated to a temperature close to a melting point of the deposited metal, for example, 400.degree. to 500.degree. C. in a case of an aluminum, the aluminum is sputtered and deposited on the substrate, and the deposited aluminum is moved on the wafer so that a greater amount of metal is deposited in a contact hole, to thus improve the step coverage.
In the high temperature heating sputtering process, the temperature of the substrate, for example, a silicon wafer, must be efficiently carried out, and therefore, a gas-assisted type sputtering device has been developed.
FIG. 1 is a schematic view of a conventional gas-assisted type sputtering device.
In a conventional high temperature heating sputtering process using the gas-assisted type sputtering device shown in FIG. 1, a substrate 10, for example, a silicon wafer, is arranged on a substrate holder 9 having a substrate supporter 17, in a vacuum chamber 1 having an exhaust gas control valve 8. Argon (Ar) gas for heating the substrate 10 is supplied through a gas supply means 4 having gas flow rate controller 7a and a needle valve 7b, while controlling the temperature of the substrate 10 by a heater controller 11 connected to a cartridge heater 3, and the argon gas is ionized by an electric discharge means 6 connected to a D.C. power source 14, so that the ions collide with a target 5 and the target material, for example, aluminum, is sputtered and deposited on the substrate 10. In FIG. 1, the numbers 12, 13, 15, and 16, denote a target fixing holder, a target supporting cooling plate, a permanent magnet, and a rotating part, respectively.
The gas-assisted type heating method in a sputtering shown in FIG. 1 is superior to the well known infrared-ray heating method in a sputtering. Namely, in this infrared process, the heating effects, i.e., the infrared ray absorption ratios, are different due to, for example, a specific resistance of the wafer and kinds of deposits thereon, and thus a control of the temperature is difficult. Such problems do not arise in the gas-assisted type sputtering process.
Nevertheless, in the high temperature sputtering process using the gas-assisted type sputtering device, the temperature of the wafer may be often varied by the kinetic energy of a sputtered target material which is deposited on a wafer, and by the kinetic energy of a secondary electron emitted from the surface of the target. Namely, the results of an experiment showed that the temperature of a wafer is increased by 100.degree. to 150.degree. C. during the sputtering process, compared with the temperature at the start of the sputtering process, as shown in FIG. 2. This increase of the temperature causes variations in the properties of the deposited material film, for example, the surface of the film is undulated or becomes white and cloudy, and the deposited film is not homogeneous in the direction of the film thickness.
Accordingly, to control the temperature of the substrate on which a target material is deposited, the temperature of the heater block 2 must be controlled, but the control response time is slow, and therefore, in the gas-assisted type sputtering device shown in FIG. 1, the amount of gas supplied is varied to improve the control response time. Nevertheless, to make an abrupt change in the temperature, the amount of gas supplied must be extremely varied, with the result that the inner pressure of the vacuum chamber is varied and thus the sputtering condition is varied.